Imaging devices, such as cameras, can be used to capture images of portions of the electromagnetic spectrum, such as the visible light spectrum, incident upon an image sensor. For ease of discussion, the term light is generically used to cover radiation across the entire electromagnetic spectrum. In a typical imaging device, light enters through an opening (aperture) at one end of the imaging device and is directed to an image sensor by one or more optical elements such as lenses. The image sensor includes pixels or sensor elements that generate signals upon receiving light via the optical element. Commonly used image sensors include charge-coupled device (CCDs) sensors and complementary metal-oxide semiconductor (CMOS) sensors.
Image sensors are devices capable of converting an optical image into a digital signal. Image sensors utilized in digital cameras are made up of an array of pixels; the number of pixels determines the megapixel rating of the image sensor. For example, an image sensor having a width×height of 2272×1704 pixels would have an actual pixel count of 3,871,488 pixels and would be considered a 4 megapixel image sensor. Each pixel in an image sensor is capable of capturing light and converting the captured light into electrical signals. In order to separate the colors of light and capture a color image, a Bayer filter is often placed over the image sensor, filtering the incoming light into its red, blue, and green (RGB) components which are then captured by the image sensor. The RGB signal captured by the image sensor plus Bayer filter can then be processed and a color image can be created.
Generally, image capture utilizes a single image sensor, to capture individual images, one at a time. A digital camera typically combines both an image sensor and processing capabilities. When the digital camera takes a photograph, the data captured by the image sensor is provided to the processor by the image sensor. Processors are able to control aspects of a captured image by changing image capture parameters of the sensor elements or groups of sensor elements used to capture the image.
The ISO/IEC 10918-1 standard, more commonly referred to as the JPEG standard after the Joint Photographic Experts Group that developed the standard, establishes a standard process for digital compression and coding of still images. The JPEG standard specifies a codec for compressing an image into a bitstream and for decompressing the bitstream back into an image.